BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to an image sensor used in an optical unit for.one-dimensionally
reading an image. More particularly, the present invention relates to a reduction
type image sensor fabricated using optical waveguides.
[0002] The present invention also relates to the design of an optical image sensor usable
in a device such as a facsimile machine, a bar code reader and a computer image input
device. More particularly, the present invention relates to the optical design of
an image scanner fabricated by using an array of optical waveguides. The present invention
discloses a new designing method in which the image sensor can be easily fabricated
and stability and performance of the image sensor in use are improved by integrating
an LED array with a waveguide substrate so as to direct light from an LED (light emitting
diode) light source onto an object.
[0003] The present invention also relates to an optical scanner for converting an image
to electronic data and is able to be utilized in a facsimile machine, a scanner used
to input compositions and figures to a computer, an optical bar code reader, etc.
[0004] The present invention further relates to an image sensor used in a one-dimensional
reading optical system of a hard copy, etc. More particularly, the present invention
relates to a reduction type image sensor using optical waveguides and a manufacturing
method of this reduction type image sensor.
2. Description of the Related Art
[0005] Recently, high performance and compactness of a one-dimensional image sensor for
converting image information to an electric signal are required as the demand for
an image reader used in a facsimile machine, an image scanner, a digital copying machine,
etc. has increased. A general one-dimensional image sensor of a facsimile machine,
etc. can be divided into two kinds of structures composed of a reduction type structure
and a contact type structure (also called an equal magnification type structure).
In the reduction type structure, a one-dimensional image is reduced in size and is
projected onto a charge coupled device (CCD) face by a lens. In the contact type structure,
a lens projects the image, with unity magnification, onto an optoelectronic detector
which corresponds one-to-one with the image. A waveguide type reduction type image
sensor utilizing an optical waveguide array instead of a lens is described in this
patent.
[0006] An LED array having LEDs arranged in a linear shape and a linear light source of
a fluorescent lamp, etc. are widely used as a light source of the image sensor.
[0007] Fig. 1 is a view for explaining the operation of a reduction type image sensor. An
original 1 is illuminated by a light emitting diode array linearly arranged or a linear
light source 7 such as a fluorescent lamp, etc. The light emitting diode is called
an LED in the following description. Reflected light from the original 1 is focused
and formed as a reduced image on a photoelectric converting element array 30 such
as a CCD, etc. by a lens 40. The photoelectric converting element array 30 converts
the image information of the original formed as the reduced image to an electric signal
of time series and outputs this converted electric signal.
[0008] Fig. 2 shows a contact type image sensor. This contact type image sensor is arranged
such that the detector of a photoelectric converting element array 31 covers the entire
reading width. Reflected light from an original 1 irradiated by a light source 7 is
incident on the photoelectric converting element array 31 directly or through a lens
array 41 so that image information is converted to an electric signal.
[0009] Japanese Patent Application Laying Open (KOKAI) No. 6-94346 shows a waveguide type
reduction type image sensor to-solve problems of the above reduction type image sensor
and the above contact type image sensor. Fig. 3 is a view schematically showing the
waveguide type reduction type image sensor. Fig. 4 is a plan view of the waveguide
type reduction type image sensor. The waveguide type reduction type image sensor has
a microlens array 4 formed along the width of the front face, an optical waveguide
substrate 2 and a photoelectric converting element array 3. Plural three-dimensional
waveguides for guiding light from an input image to the photoelectric converting element
array are formed in the optical waveguide substrate 2. In the following description,
each of the three-dimensional waveguides is simply called a waveguide. The waveguide
type reduction type image sensor obtains a reduced image by setting the waveguide
pitch at the emitting end of the waveguide to be narrower than the waveguide pitch
at the incident end of the waveguide. In the waveguide type image sensor, a coupling
optical system, the optical waveguide substrate and the photoelectric converting element
array are integrated with each other so that subsequent alignment or adjustment is
not necessary. Further, this integrated waveguide type reduction type image sensor
has excellent shock resistance and cost thereof can be reduced.
[0010] Resolution of the reduction type image sensor shown in Fig. 1 is determined by lens
performance and the pixel pitch of the photoelectric converting element array 30.
In the case of a reading resolution of 200 dpi (200 dots per one inch) and a reading
width of 256 mm, the distance (optical path length) d between the original 1 and the
photoelectric converting element array 30 is about 330 mm. Cost of the reduction type
image sensor is low and a reading operation of this reduction type image sensor can
be performed at a high speed. However, element sizes in the reduction type image sensor
are large since light is converged by the lens 40. Therefore, no reduction type image
sensor can be made compact. Further, it is complicated to adjust the optical system
of the reduction type image sensor.
[0011] In contrast to this, in the contact type image sensor, the distance (optical path
length) d from the original 1 to the photoelectric converting element array 31 is
short. The photoelectric converting element array has a large size and is thus expensive,
and it is necessary to arrange a complicated electronic circuit for operating the
photoelectric converting element array. Therefore, it is difficult to reduce cost
of the contact type image sensor.
[0012] In the construction of the waveguide type image sensor shown in Fig. 4, the noise
level is increased and the S/N ratio (a signal/noise ratio) is reduced when stray
light caused by light scattering from irregularities of the light coupling portion
(the waveguide incident end face) to the waveguide and the waveguide side is incident
on the photoelectric converting element array 3.
[0013] The light source is constructed by using the LED array in which, for example, 27
LEDs are arranged linearly along the original face width. As shown in Fig. 3, the
light source is arranged in a position in which generated light is incident on the
original at 45 degrees. The LED array has a structure in which the original is directly
irradiated from a point light source. Accordingly, it is difficult to make the LED
array compact. Further, there are problems of non-uniform irradiation, large energy
loss caused by spreading of the irradiated light, etc. and further, it is difficult
to operate the LED array with low voltage and reduce power consumption of the LED
array.
[0014] A waveguide type image sensor is fabricated by utilizing an optical waveguide array
formed on a plastic or glass substrate. Light scattered from an image is first coupled
into the waveguide array by using an array of microlenses. Then, this light is transmitted
to a CCD (charge coupled device) type detector through a waveguide. A light source
of this type of device is constructed by an array of LED light emitting devices.
[0015] In this type of device, an array of optical waveguides is fabricated on a glass or
plastic substrate. Light spread from an image is first coupled into the array of optical
waveguides. Thereafter, this light is transmitted to an optical detector of a CCD
type through these waveguides.
[0016] An LED array emitting 570 nm light is used as the light source. In a typical case,
the LED array is fixed at an oblique angle (about 45 degrees) to an object plane at
a distance typically from 5 mm to 10 mm depending on the design of the scanner. The
LED light emitting device is characterized in that light is not unidirectional, but
spreads out over a wide region. A typical diode has peak emission at 30 degrees to
its normal and its intensity does not drop to 50 % of the peak until 85 degrees from
the normal.
[0017] Further, in the general system, all optical systems of the LED array and the detector
are separately arranged so that there is a danger of mis-alignment of these optical
systems.
[0018] At present, the optical scanner has two kinds of general constructions as shown in
Figs. 5 and 6. A light source is constructed by an array of light emitting diodes
(LEDs) or a light emitting tube of a fluorescent type and irradiates an object portion
71 on a page or line to be scanned. For example, in a first general example shown
in Fig. 5, light reflected from the object 71 is normally converged onto a single
photodetector 73 such as a charge coupled device (CCD) by a lens or a lens system
72. Resolution of this system is determined by the spacing of pixels on the CCD and
performance of the lens. In the case of a scanner in a facsimile machine, a resolution
of 200 dots per inch is used. In this construction, the distance d between the object
and the detector is relatively large. For example, this distance d is set to about
330 mm with respect to a scan width of 256 mm. As shown in Fig. 6, a device utilizing
three mirrors for reflecting light reflected from the object is used to shorten the
length of the optical system. Light paths efficiently overlap each other by these
mirrors so that the distance between an image and the detector can be reduced. Therefore,
an actually used minimum distance between the object and the detector is 83 mm so
that the scanner is made considerably compact in comparison with the scanner shown
in Fig. 5.
[0019] Japanese Patent Application Laying Open (KOKAI) No. 7-30716 shows an original reader
in which image information of an original is reduced by an optical waveguide arranged
in a sector shape by reducing the waveguide pitch on the emitting side of the device
with respect to the pitch on the incident side of the device. This original reader
is compact and it is not necessary to adjust the optical axis in comparison with a
device for reducing an image by using the above lens and mirrors.
[0020] In the original reader shown in Japanese Patent Application Laying Open (KOKAI) No.
7-30716, the optical waveguides are arranged in a sector shape. Accordingly, when
the angle between the waveguide and the front face of the waveguide substrate is small,
reflected light from the object is not efficiently coupled into the waveguide and
output light from the waveguide is not efficiently coupled out of the waveguide. In
order to maintain reasonable coupling efficiencies the angle between the waveguide
and the front face of the waveguide substrate must be kept large. Consequently, it
is not possible to have a high image reduction rate while maintaining compact size.
[0021] A reduction type image sensor using plural optical waveguides has been recently proposed.
For example, Japanese patent application No. 6-94346 shows a waveguide type reduction
type image sensor having a lens, an optical waveguide substrate and a photoelectric
converting element array. The lens is formed along the width of the front face. The
optical waveguide substrate has plural waveguides formed such that these waveguides
guide light converged by this lens. Light guided by these plural waveguides is incident
on the photoelectric converting element array. Cost of this image sensor is low and
elements of this image sensor can be made compact. Further, it is not necessary to
adjust the optical system of this image sensor.
[0022] Several methods for manufacturing a polymeric optical waveguide using a polymeric
material as a core which can be used in such a reduction type image sensor are proposed.
[0023] In a first manufacturing method, a patterned substrate composed of a polymeric material
such as PMMA, etc. and having the pattern of a groove constituting a capillary is
manufactured by using a normal injection moulding machine. Next, the grooved portion
of the manufactured patterned substrate is filled with a polymeric precursor material
as a polymeric raw material for the core of the waveguide. A plane substrate constructed
by a polymer such as PMMA, etc. then comes in close contact with the grooved portion
of the patterned substrate. Thereafter, the grooved portion is polymerized by irradiation
of an ultraviolet ray, etc. so that the core of the optical waveguide constructed
by the polymeric material is formed.
[0024] Japanese patent application No. 6-300807 shows another manufacturing method of the
polymeric optical waveguide. In this manufacturing method, the patterned face of the
patterned substrate having the pattern of a groove constituting a capillary comes
in close contact with the plane substrate so that the capillary is formed by this
groove. Thereafter, this capillary is filled with a monomer solution as the raw material
of the core of the optical waveguide by a capillary phenomenon. Then, this monomer
solution is polymerized. In this manufacturing method, no gap is formed on the boundary
between the patterned substrate and the plane substrate. Accordingly, there is no
crosstalk caused by leaked light between cores so that a polymeric optical waveguide
having excellent optical waveguide characteristics can be realized.
[0025] The general reduction type image sensor using a lens system requires a long optical
path length between an original face and a solid-state image sensor. Therefore, it
is difficult to make the reduction type image sensor compact. Further, when the image
sensor is fabricated, it is necessary to adjust the optical system every image sensor.
Furthermore, the reduction type image sensor is weak in vibration.
[0026] In the general contact type image sensor, the photoelectric converting array has
the same size as the original width. Accordingly, the S/N ratio of the photoelectric
converting signal is reduced and it is difficult to operate the contact type image
sensor at a high speed because of a parasitic capacitance between wirings in a certain
case.
[0027] In the reduction type image sensor using optical waveguides, elements can be made
compact and no adjustment of the optical system is required in comparison with the
above two image sensors. Further, cost of the reduction type image sensor is very
low and the reduction type image sensor has high performance and can be made compact.
However, there is some loss of the optical signal in the bent portion of each of the
waveguides indispensable to a reduction in the size of an original image.
[0028] A manufacturing method of the optical waveguide has the following problems.
[0029] The optical waveguide manufactured by the first manufacturing method described in
the prior art is formed by filling the patterned substrate with a core material and
sticking the patterned substrate and the plane substrate together. Therefore, a polymeric
material for the core is polymerized in a projecting state between the plane substrate
and the patterned substrate so that a thick layer approximately ranging from 1 to
10 µm is formed. Accordingly, when light is incident on the optical waveguide, this
light is leaked to the layer and is diffused to the entire device. In contrast to
this, if the optical waveguide is manufactured by using the second manufacturing method
described in the prior art, the core material is drawn up after the patterned substrate
and the plane substrate are stuck together. Therefore, there is no layer between the
patterned substrate and the plane substrate so that no light is leaked between cores.
[0030] Loss of the optical signal in the bent portion of the optical waveguide can be reduced
by forming a groove filled with a substance having a refractive index lower than that
of a peripheral substrate outside this bent portion. These results are confirmed by
simulation and are described in "J.Yamauchi et al:'Beam-Propagation Analysis of Bent
Step-Index Slab Waveguides', ELECTRONICS LETTERS,1990, Vol.26, No.12, p822-p824".
[0031] EP-A-0 297 798 relates to a contact-type image sensor having a substrate disposed
between photodetectors and a manuscript and having optical fibres buried in the substrate
for transmitting light to the photodetectors.
[0032] EP-A-0 285 351 relates to an S-shaped waveguide in a substrate.
[0033] US-A-3767445 discloses a substrate constructed from a polymer and optical wave guides
constructed from a polymer having a higher refraction index.
SUMMARY OF THE INVENTION
[0034] It is desirable to provide a compact scanner for increasing the reduction rate of
an image while reducing the distance between the object and the detector, and having
a simple structure which can be cheaply manufactured.
[0035] The present invention provides a compact optical scanner as set out in claim 1. Preferably,
each of the waveguides has two bent portions having a bending angle of 90 degrees.
Accordingly, even when the image reduction ratio is large, the distance between the
object and a detector can be made small.
[0036] Preferably, a microlens integrated with the substrate is fabricated in alignment
with the end portion of each of the optical waveguides on the substrate face opposite
to the object so that each image portion can be reliably converged to each of the
waveguides.
[0037] Preferably, the numerical apertures of the microlens and the polymer of each of the
optical waveguides are set to be equal to each other. Accordingly, it is ensured that
only light scattered from a scanned image portion is incident on each of the waveguides.
[0038] Further objects and advantages of the present invention will be apparent from the
following description of the preferred embodiments of the present invention as illustrated
in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039]
Fig. 1 is a view for explaining a general reduction type image sensor;
Fig. 2 is a view for explaining a general contact type image sensor;
Fig. 3 is a view for explaining a general waveguide type reduction type image sensor;
Fig. 4 is a plan view showing the construction of the waveguide type reduction type
image sensor shown in Fig. 3;
Fig. 5 is a schematic view showing the construction of a general optical scanner;
Fig. 6 is a view for explaining the operation of an optical system used in the general
optical scanner;
Fig. 7 is a view showing detectors arranged in the general optical scanner;
Fig. 8 is a view showing the construction of a waveguide type image sensor in accordance
with a first example;
Fig. 9 is a plan view showing the construction of a photodetecting section of the
waveguide type image sensor shown in Fig. 8;
Fig. 10 is a plan view showing the construction of the photodetecting section in accordance
with a second example of a waveguide type image sensor ;
Fig. 11 is a plane view showing the construction of a waveguide type light source
shown in Fig. 8;
Figs. 12a and 12b are views showing the waveguide type light source of Fig. 8 in detail;
Fig. 13 is a plan view showing the construction of a waveguide type light source shown
in Fig. 10;
each of Figs. 14a and 14b is a graph showing the emitted light pattern from the
photodetecting section of Fig. 8;
Fig. 15 is a cross-sectional view showing one example of the construction of an image
sensor ;
Fig. 16 is a cross-sectional view showing another example of the construction of an
image sensor ;
Fig. 17 is a cross-sectional view showing another example of the construction of an
image sensor ;
Fig. 18 is a view showing travel of light within a substrate of an image sensor ;
each of Figs. 19a and 19b is a view showing another example of a construction of
or image sensor ;
Fig. 20 is a cross-sectional view showing one example of the construction of the substrate
of the image sensor;
Figs. 21a to 21f are views showing a manufacturing method of the waveguide section
of the image sensor;
Fig. 22a to 22c are views showing an optical scanner in accordance with another embodiment
of the present invention;
each of Figs. 23a and 23b is a graph showing the relation between the bending angle
of a bent portion of a waveguide in the optical scanner of Fig. 22 and the width of
this optical scanner;
Fig. 24 is a view for explaining the operation of a microlens arranged in the optical
scanner of Figs. 22a to 22c;
Figs. 25a and 25b are views showing a waveguide type reduction type image sensor in
accordance with another example;
Figs. 26a to 26e are views showing the first stage for manufacturing waveguides shown
in Figs. 25a and 25b;
Figs. 27a and 27b are views showing the second stage for manufacturing the waveguides
shown in Fig. 25a and 25b;
Figs. 28a and 28b are views showing the third stage for manufacturing the waveguides
shown in Figs. 25a and 25b;
Fig. 29 is a graph showing the reducing effects of light loss with respect to the
width of a groove arranged outside a bent portion of each of the waveguides;
Fig. 30 is a graph showing the reducing effects of light loss with respect to the
distance between a waveguide core portion and the groove arranged outside the bent
portion of the waveguide core portion; and
Fig. 31 is a graph showing the reducing effects of light loss with respect to the
difference in specific refractive index between the waveguide core portion and the
material of a clad portion.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Examples of a waveguide type reduction type image sensor and a manufacturing method
thereof will next be described in detail with reference to the accompanying drawings.
[0041] Each of the following embodiments is an example applied to a one-dimensional image
sensor (having a scan width of 256 mm corresponding to paper sheet B4) for a G3 type
facsimile machine having a resolution of 200 dpi. A photoelectric converting element
of type µ PD3743D manufactured by Nippon Denki (NEC) Co., Ltd. in Japan and having
a pitch of 14 µm and 2048 pixels.
[0042] Fig. 8 is a view for explaining the construction of a waveguide type reduction type
image sensor in accordance with a first example . The waveguide type image sensor
of Fig. 8 is constructed with a waveguide type photodetecting section and a waveguide
type linear light source.
[0043] Fig. 9 is a plan view showing the construction of the waveguide type photodetecting
section of the image sensor shown in Fig. 8. The photodetecting section is constructed
with a microlens array 4, an optical waveguide substrate 2 and a CCD (charge coupled
device) array 3. The microlens array 4 converges reflected light from an original
1 onto the incident face of the optical waveguide substrate 2. The optical waveguide
substrate 2 has an optical waveguide for guiding the converged light to the CCD array
3. The CCD array 3 is a photoelectric converting element for converting the guided
light to an electric signal and outputting this electric signal.
[0044] The optical waveguide substrate 2 is 270 mm x 25 mm x 2 mm in size and has 2048 waveguides.
The pitch of the respective waveguides on the incident end face 21 is 127 µm. The
waveguides are formed in the shape of a character L such that the waveguides are perpendicular
to the incident face 21 and the emitting face 22 which is perpendicular to this incident
face 21. The pitch of the respective waveguides on the emitting end face is 14 µm.
The core portion of the waveguides is formed in a rectangular shape 8 µm in width
and 8 µm in depth. The radius of curvature of the bent portion 23 of each of the waveguides
is 2mm.
[0045] Each of the waveguides is manufactured by a capillary method shown in Japanese Patent
Application Laying Open (KOKAI) 6-300807.
[0046] For example, PMMA (polymethyl methacrylate) is used as a waveguide substrate material
(a waveguide clad portion). Further, DAI (diallyl isophthlalate) having a refractive
index larger than that of PMMA is used as a waveguide core material.
[0047] Firstly, a rectangular waveguide groove having 8 µm in width and 8 µm in depth is
formed on the substrate having the above pattern by an injection moulding method so
that a patterned substrate is manufactured. Next, as shown in Figs. 27a and 27b, the
patterned substrate and a plane substrate (a PMMA substrate) are clamped by a jig
such that a waveguide face side of the patterned substrate comes in close contact
with the plane substrate.
[0048] The waveguide groove is filled with a monomer solution using a DAI monomer including
5 % of benzoyl peroxide. The clamped substrate and the monomer solution are placed
within a vacuum chamber. Gases are discharged from the interior of the vacuum chamber
until a vacuum degree of 10
-4 Torr is achieved. Thus, degassing processing of the DAI monomer solution is performed.
Thereafter, one open end of the above clamped substrate is dipped into the monomer
solution. Then, the interior of the vacuum chamber is leaked such that the pressure
within the vacuum chamber is gradually changed from a vacuum to atmospheric pressure.
Thus, the waveguide groove is filled with the monomer solution. Thereafter, the clamped
substrate is heated for six hours at a temperature of 85 °C by an oven so that the
DAI monomer solution is polymerized. Then, the clamped substrate is detached from
the clamp jig and the incident end face and the emitting end face of the clamped substrate
are polished so that an optical waveguide substrate is manufactured.
[0049] With respect to the polymeric optical waveguide manufactured in this first embodiment,
the PMMA polymer has a refractive index of 1.49 and the DAI has a refractive index
of 1.59. Accordingly, a numerical aperture (NA) of this optical waveguide is estimated
as 0.55 from the following formula.
![](https://data.epo.org/publication-server/image?imagePath=2003/37/DOC/EPNWB1/EP96305150NWB1/imgb0001)
[0050] Propagating loss of this waveguide is about 0.1 dB/cm.
[0051] Similar to the waveguide pitch, the microlens array 4 is constructed such that 2048
microlenses having 127 µ m in diameter are arranged in a linear shape over a length
of 256 mm (an original width of sheet size B4).
[0052] It is theoretically known that 84 % of the entire amount of parallel light incident
on a microlens is converged in the shape of a disc having a diameter w and shown by
the following formula (1).
![](https://data.epo.org/publication-server/image?imagePath=2003/37/DOC/EPNWB1/EP96305150NWB1/imgb0002)
[0053] Here, NA is the numerical aperture of the above microlens and λ is a wavelength of
light and is set to 570 nm. The microlens is 0.15 in NA so that light is converged
to a spot size, w, of 4.6 µm in diameter. The glass substrate used in the microlens
is 0.45 mm in thickness such that light is converged onto the incident end face of
the optical waveguide substrate.
[0054] As mentioned above, the numerical aperture (NA) of the microlens is 0.15 and the
NA of the waveguide is 0.55. Accordingly, there is no light coupling loss caused by
mismatching of the numerical apertures (NAs) so that reflected light from an original
face can be ideally coupled into the waveguide by the microlens.
[0055] The above optical waveguide substrate 2, the microlens array 4 and the CCD array
3 are adhered to each other through an optical adhesive having a refractive index
close to that of this substrate so that a photodetecting section is manufactured.
For example, this optical adhesive is an ultraviolet ray curing type LA-3556 manufactured
by Toyo Ink Seizo Co., Ltd.
[0056] Figs. 14a and 14b show measured results of the waveguide output light pattern to
verify effects of the photodetecting section in the above first embodiment. The light
source uses a general LED array and the reflected light of a white original is detected.
Fig. 14a shows the output light pattern of the photodetecting section.
[0057] Fig. 14b shows the output light pattern of a general type photodetecting section
shown in Fig. 4. The general type photodetecting section has a large noise level and
a small C/N (carrier/noise) ratio. In contrast to this, the photodetecting section
in the first example has a peak intensity of signal light equal to that of the general
type, but has a low noise level so that a large C/N ratio is obtained in comparison
with the general type. The noise level in the general type is high because of stray
light caused by waveguide uncoupled light from the light source, etc. In the photodetecting
section, influences of the above stray light can be reduced so that the C/N ratio
is improved. Accordingly, it should be understood that the photodetecting section
of the present invention is effective to improve a S/N (signal/noise) ratio.
[0058] Fig. 11 is a plan view showing the construction of the waveguide type linear light
source. Each of Figs. 12a and 12b is an enlarged view showing a structure around the
light source portion 6. The waveguide type linear light source is constructed with
the light source portion 6 and an optical waveguide substrate 5 composed of waveguides
and a planar waveguide.
[0059] The optical waveguide substrate 5 is 270 mm x 30 mm x 2 mm in size and is constructed
by plural L-shaped waveguides 51 and a planar waveguide 52 formed along an original
face width (260 mm).
[0060] Each of the L-shaped waveguides 51 has a planar waveguide coupling portion 53 and
a waveguide 55 bent 90 degrees such that the waveguide 55 is perpendicular to an LED
light incident face 54. In the first example, 13 L-shaped waveguides are formed at
an interval of 20 mm at the emitting end (in a planar waveguide coupling portion).
Further, tapered waveguides 56 are formed on the incident side such that each of the
tapered waveguides 56 is wide on its incident end face and is narrow at its L-shaped
waveguide coupling end. The widening angle of a tapered portion of each of the tapered
waveguides 56 is set to one degree. Here, similar to the photodetecting section, each
of the plural L-shaped waveguides is formed with a rectangular shape 8 µm x 8 µm in
size.
[0061] The L-shaped waveguides have different lengths so that light losses until the planar
waveguide coupling portions are different from each other. Therefore, when the same
light amount is waveguided, the emitted light amount is changed depending on a waveguide
length. An open width d1 on an end face of each of the tapered waveguides is set to
be narrow with respect to a waveguide located near the light source and having a small
propagating loss in the L-shaped waveguides, and is set to be wide with respect to
a long L-shaped waveguide such that the light amount in the planar waveguide coupling
portion is constant for a uniform irradiated light amount.
[0062] The open width d1 of a tapered waveguide can be designed from the L-shaped waveguide
length and the waveguide propagating loss. For example, in the first example, the
open width is about 530 µm with respect to an L-shaped waveguide 56a nearest the light
source and is about 550 µm with respect to an adjacent L-shaped waveguide 56b, and
is about 920 µm with respect to a longest L-shaped waveguide 56c. The length of the
tapered portion and a waveguide interval are respectively changed in accordance with
the open width of the tapered waveguide and can be designed from the widening angle
(one degree on one side) of the tapered portion and the waveguide open width. For
example, in the first example, the length of the tapered portion of the L-shaped waveguide
56a is 1.52 mm and the length of a tapered portion of the L-shaped waveguide 56b is
1.58 mm. Further, the waveguide interval is 540 µm.
[0063] As shown in Fig. 11, the planar waveguide 52 is formed such that the planar waveguide
52 has a waveguide coupling face width of 240 mm, an emitting end width of 260 mm
and a width of 15 mm. Tapered portions are formed at both ends of the planar waveguide
52. As already mentioned above, 13 L-shaped waveguides are coupled into each other
at an interval of 20 mm on the waveguide coupling face 53. Light from each of the
L-shaped waveguides is emitted from the planar waveguide 52 at an angle of 33 degrees
on one side. The planar waveguide width is designed such that the widening width of
the L-shaped waveguide emitted light on the planar waveguide emitting face is 20 mm
equal to the L-shaped waveguide interval to equalize the light amount on the planar
waveguide emitting face. Accordingly, the planar waveguide width can be reduced by
reducing the interval of the L-shaped waveguides coupled into the planar waveguide.
Namely, the planar waveguide width can be reduced by increasing the number of waveguides.
For example, if the waveguide interval is 10 mm and the number of waveguides is 26,
the planar waveguide width can be set to about 7. 5 mm.
[0064] The light source portion 6 is constructed from an LED array 61 having plural LEDs
arranged in a linear shape and a cylindrical lens 62. The light source portion 6 is
arranged on the incident end face of the optical waveguide substrate 5. Figs. 12a
and 12b are views showing the schematic construction of the incident face of the LED
array. In the light source portion in the first embodiment, 5 LEDs are linearly arranged
and light is converged in a stripe shape by the cylindrical lens having a numerical
aperture of 0.15.
[0065] In the above construction, light from the light source portion is converged onto
the incident face of the optical waveguide substrate having the tapered waveguides
by the cylindrical lens. This light is waveguided along an L-shaped waveguide and
is propagated within the planar waveguide at the widening angle determined by the
waveguide numerical aperture (NA) so that this light is uniform. This light is then
emitted from the end face of the planar waveguide.
[0066] Similar to the photodetecting section, the optical waveguide substrate is manufactured
by the above-mentioned construction using the capillary method described in Japanese
Patent Application Laying Open (KOKAI) No. 6-300807.
[0067] Distributions of illuminance (L) in the waveguide type light source in the first
example and the general LED array light source are measured for comparison. This general
LED array light source has a structure in which 27 LEDs are linearly arranged at an
equal interval. An illuminance deviation ΔL is defined by the following formula.
![](https://data.epo.org/publication-server/image?imagePath=2003/37/DOC/EPNWB1/EP96305150NWB1/imgb0003)
[0068] A maximum illuminance deviation in the general type is about 18 %. In contrast to
this, the maximum illuminance deviation in the waveguide type light source is about
10 %. Accordingly, it should be understood that the irradiated light amount distribution
is improved.
[0069] In the photodetecting section in the above first example, it is possible to prevent
a signal from being deteriorated as the uncoupled light is not incident on the photoelectric
element. Further, a bent portion of the waveguide is formed in only one place in comparison
with the construction of the waveguide type image sensor of Fig. 4 so that light loss
in the waveguide bent portion can be reduced.
[0070] In accordance with the waveguide type light source in the above first example, it
is possible to obtain a linear light source having a small deviation in irradiated
light amount and a uniform irradiated light amount. Further, the number of LEDs can
be reduced so that power consumption of the image sensor can be reduced. Further,
the image sensor can be made thin in comparison with the general light source in which
LEDs are arranged at an equal interval. Accordingly, the image sensor can be made
compact and light in weight by combining the light source with the waveguide type
photodetecting section.
[0071] Further, it is not necessary to fabricate and adjust the light source by integrating
the light source so that a manufacturing process of the image sensor can be simplified.
Further, it is possible to provide an image sensor having excellent shock resistance.
[0072] Furthermore, an optical waveguide corresponding to a large original width can be
easily manufactured at low cost by an ion diffusion method, an injection moulding
method, etc.
[0073] A second example of a waveguide type reduction type image sensor will next be explained
with reference to Figs. 10 and 13, etc.
[0074] Each of Figs. 10 and 13 is a plan view for explaining the construction of the waveguide
type reduction type image sensor in the second example. Fig. 10 shows a photodetecting
section in which a photoelectric converting element array is divided into two sections
and 1024 waveguides are coupled into each of the divided sections. Thus, the width
of a waveguide substrate can be reduced from 25 mm to 12.5 mm.
[0075] Fig. 13 shows a waveguide type light source. Similar to the photodetecting section,
waveguides are divided by dividing a light source portion into two sections so that
the width of a waveguide substrate can be reduced from 25 mm to 20 mm. Further, as
mentioned in the first example, the width of the waveguide substrate can be set to
17. 5 mm if the number of waveguides is doubled and a coupling waveguide interval
is set to 10 mm. The longest waveguide length can be also reduced by half by dividing
the light source into two sections so that waveguide loss can be reduced by half.
[0076] As mentioned above, the waveguides can be divided in two directions so that the waveguide
type reduction type image sensor can be made further compact.
[0077] In a waveguide type reduction type image sensor as described above, it is possible
to prevent a signal from being deteriorated as the uncoupled light is not incident
on the photoelectric element. Further, a bent portion of the optical waveguide is
formed in only one place in comparison with the construction of a general waveguide
type image sensor so that light loss in the waveguide bent portion can be reduced.
[0078] Also, the construction of a photodetecting means is simplified and the cost of the
waveguide reduction type image sensor can be reduced.
[0079] Optical waveguides can be divided into right-hand and left-hand sections and can
be arranged on the right-hand and left-hand sides. Accordingly, the width of an optical
waveguide substrate can be reduced and the propagating loss of a longest waveguide
can be reduced by half.
[0080] Also, a light source means can be made compact and/or thin.
[0081] It is possible to obtain a uniform irradiated light intensity distribution and the
light of a light emitting element can be efficiently used. Accordingly, the number
of light emitting elements can be reduced and power consumption of the waveguide type
reduction type image sensor can be reduced.
[0082] Optical waveguides can be divided into right-hand and left-hand sections and can
be arranged on the right-hand and left-hand sides. Accordingly, the width of an optical
waveguide substrate can be reduced and the propagating loss of the longest waveguide
can be reduced by half.
[0083] A photodetecting means and a light source means may be integrated with each other
so that the image sensor can be made compact. Further, since a coupling optical system,
an optical waveguide substrate, a photoelectric converting element and a light source
are integrated with each other, it is not necessary to adjust the image sensor so
that the manufacturing process of the image sensor can be simplified and the image
sensor has excellent shock resistance.
[0084] Further, the optical waveguides arranged in the optical waveguide substrate of the
light source means/the photodetecting means can be easily manufactured by an ion diffusion
method, an injection moulding method, etc. such that each of the optical waveguides
has an arbitrary size. Accordingly, an image sensor corresponding to an original width
can be manufactured at low cost.
[0085] An LED array can be arranged in various kinds of forms. Figs. 15 to 17 show different
arrangements of an image sensor in which LEDs are attached to a waveguide substrate.
Each of Figs. 15 and 16 is a cross-sectional view of the substrate in its width direction.
Fig. 17 is a cross-sectional view of the substrate in its longitudinal direction.
[0086] In Fig. 15, a CCD element 103 for reading an image is attached to the rear portion
of the substrate shown on the left-hand side. Further, an LED 104 as a light source
is directly attached to this rear portion of the substrate. Light outputted from the
LED is directly coupled into the substrate and travels along the substrate while this
light is reflected many times within the substrate as shown in Fig. 18. In this way,
the substrate functions as a planar light pipe. The substrate has a refractive index
of about 1.5 and air has a refractive index of 1.0. Internal total reflection occurs
for all angles at which an angle θ shown in Fig. 18 is less than 48.2 degrees. In
this case, light is transmitted within the substrate. Light outputted from the LED
is emanated, but about 90 % of all light outputs outputted by a typical LED is included
within an angle of plus or minus 48.2 degrees. When the light
reaches the front face end portion of the substrate shown on the right-hand side of Fig.
15 and shaped so as to form a cylindrical lens 105, this light is outputted from the
substrate. This shape has the effect of focusing the light onto an object. A linear
microlens array 106 is arranged on the crest of the cylindrical lens in a longitudinal
direction of the substrate so as to detect light reflected from the object. The pitch
of the microlens array is accurately matched to that of the waveguide array. The reflected
light from the object is coupled into a waveguide by this microlens. The microlens
array typically has a diameter of 125 µm. Accordingly, the microlens array has little
influence on the operation of the cylindrical lens typically being several millimeters
in diameter.
[0087] Fig. 16 shows an arrangement in which an LED array is attached to a side face (a
lower portion in Fig. 16) of the substrate. In this case, an angled reflecting plate
108 is arranged within the substrate. This reflecting plate is coated with a metal
having a light reflecting property such as aluminum and formed by evaporation or sputtering.
Light from the LED is first incident on the angled reflecting plate. The propagating
direction of this light is turned such that this light travels along the substrate.
Thereafter, this light is reflected within the substrate as described in the previous
example. Since the angled reflecting plate can be easily formed by injection moulding,
this method is particularly suitable for a plastic substrate. It also has the advantage
that an LED light source and a CCD detector are attached onto different faces of the
substrate. Namely, it is possible to use a thinner substrate in a vertical direction
in Fig. 16 from a purely geometrical aspect.
[0088] Fig. 17 shows a configuration in which two LED array light sources are used. These
two LED array light sources are arranged along the side end portions of the substrate.
This configuration is also beneficial because an LED array 104 and a CCD detector
103 are separated from each other and the substrate can be made thinner. The side
end portion of the substrate is angled such that light is projected forward onto an
object. The change in intensity of light outputted from the front face of the substrate
on the left-hand side of Fig. 17 is made uniform by changing the intensity of the
LED light emitting body within the LED array. This can be achieved by simply arranging
series resistors having suitable resistance values in the LED circuit. It is necessary
to set the voltage of an LED in a central portion of the substrate to be higher than
a voltage provided by light of the LED in an end portion of the substrate.
[0089] In all these cases, the LED can be firmly attached to the substrate. Accordingly,
when the LED array is used, there is no risk of mis-alignment caused in a general
system in which all optical systems of lenses and a detector are separately arranged.
[0090] The following explanation relates to a manufacturing method of an optical device
in which an injection moulded polymeric substrate is used to fabricate optical waveguides
for transmitting light from the LED array to a scanned object through an integrated
circular lens.
[0091] A waveguide pattern shown in Figs. 19a and 19b is formed in a PMMA substrate (Acrypet
supplied by Mitsubishi Rayon Company of Japan) by injection moulding. The groove for
forming each of waveguides is 8 µm x 8 µ m in size. If this groove is filled with
a polymer of different refractive index, this groove forms multimode type waveguides.
The waveguides are arranged on the front face of the substrate at an interval of 125
µm in the longitudinal direction of the substrate. This corresponds to a resolution
of 200 dots per inch which is the standard for current facsimile machines. The input
face of the substrate is shaped as follows. Namely, the entire shape of the input
face of the substrate firstly forms the lower half of a cylindrical lens. Secondly,
an array of microlenses having 125 µm in diameter and pitch is formed along an upper
end portion of the substrate. The position of each of the microlenses is precisely
aligned with that of the groove forming each of the waveguides so that light is coupled
into the waveguide. Each of the microlenses is slightly projected from the remaining
portion of the substrate so as to eliminate a joining portion formed when an upper
half of the substrate is assembled. Fig. 20 shows a lower substrate design. Fig. 20
also shows a groove having an angle of 45 degrees and formed on the lower side of
the substrate and forming a reflecting plate.
[0092] Then, the substrate is placed in a vacuum evaporator so that the substrate is coated
with an aluminum layer having 100 nm in thickness in a region of the angled groove.
Although normal evaporation procedures are used, the substrate is arranged within
a chamber and is masked such that only the angled surface of the substrate is coated
with the aluminum layer.
[0093] The upper half of the substrate is also formed from a similar material by injection
moulding, but this formation is not described here.
[0094] A manufacturing method of the substrate will next be explained with reference to
Figs. 21a to 21f.
[0095] The upper and lower halves of a substrate are assembled and seams of the substrate
are joined to each other by ultrasonic welding as shown in Figs. 21a and 21b. In the
ultrasonic welding, a polymer is melted such that peripheral portions of end portions
of the substrate are sealed.
[0096] The grooves within the substrate are filled with RAV7 supplied by Mitecs, Japan.
15 ml of RAV7 is first mixed with 0.58g of benzoyl peroxide functioning as a polymerizing
catalyst. The filling method is shown in Figs. 21c, 21d and 21e. As shown in Fig.
21c, a monomer mixture is first placed in a 10
-4 Torr vacuum for 15 minutes to degas. Then, the substrate is arranged together with
the monomer mixture within a vacuum chamber. In Fig. 21d, the vacuum chamber is evacuated
for 30 minutes. Then, the sample is lowered into the polymer mixture in a state in
which the open ends of the grooves are set to a lower side. In Fig. 21e, the pressure
within the vacuum chamber is gradually raised to atmospheric pressure. The pressure
within the groove is lower than that around the monomer so that the monomer is raised
along the groove. When the groove is filled with the monomer, the sample is placed
in an oven at 80°C for 6 hours in Fig. 21f. During this time, the monomer polymerizes
and forms a solid monomer.
[0097] An end face of the substrate on a side opposed to a shaped end portion is located
on the open end side of a waveguide and is polished using alumina polishing powder
with grit down to 0.2 µm. A CCD line sensor (NEC µ PD3743D type without cover window)
is then aligned and is attached to this end face of the substrate by using optical
epoxy.
[0098] As mentioned above, a large part of the light emitted by an illuminating device is
transmitted to the face of the substrate opposite to the object by total internal
reflection within the substrate so that the object is efficiently illuminated.
[0099] In accordance with a ninth construction of the present invention. The substrate may
be constructed with a convex face on the face opposite to the object thus forming
a cylindrical lens. Accordingly, light transmitted within the substrate is converged
to the object so that the object is further efficiently illuminated. Further, a light
source may be integrated with a waveguide and an end face of the waveguide constitutes
the cylindrical lens. Accordingly, it is not necessary to align the light source and
the object so that the image sensor can be stably used.
[0100] The illuminating device may be arranged on a face separated from a face with aligned
CCD elements so that the substrate can be made thin.
[0101] Figs. 22a to 22c are views showing the schematic construction of an optical scanner
of an embodiment of the present invention. A scanned object 201 is illuminated by
a light source similar to a general light source. Reflected light from the object
201 is incident on an array of microlenses 205. Each of the microlenses 205 focuses
and forms one portion of the object as an image on one end face of a waveguide. Light
from a single horizontal portion of the object is transmitted through a waveguide
array and is incident onto a linear type CCD detector 203. The object is moved in
a direction perpendicular to the microlens array. Each of horizontal lines of the
image is repeatedly scanned so that the entire object is scanned. The resolution of
the scanned image in a horizontal plane is determined by the size and pitch of the
microlens and waveguide arrays. In a G3 type facsimile machine, a resolution of 200
d.p.i. (dot/inch) is required. This resolution corresponds to 125 µm in diameter of
the microlens and pitches of the microlens and the waveguide. The size and pitch of
the microlens can be reduced to improve resolution as in a computer image scanner
so that a resolution of 600 d.p.i. can be easily achieved. The resolution is determined
by the microlens size and a scan speed in the vertical direction.
[0102] A planar type optical waveguide is fabricated by various kinds of methods able to
be realized by those skilled in the art. For example, a polymeric material capable
of forming the waveguide is fabricated by using a method based on injection moulding.
In this process, a polymeric substrate having a groove is made by injection moulding.
A monomer such as an optical epoxy, etc. is spread on the substrate so that this groove
is filled with the monomer. A separate polymeric cover is placed on this substrate
and is held while the monomer is polymerized or the epoxy is cured. In this process,
a waveguide pattern is prescribed by the groove shaped in the polymeric substrate.
The material for filling the groove is selected such that this material has a refractive
index higher than that of the polymeric substrate and the filled groove becomes an
optical waveguide. The polymeric substrate can be manufactured at. low cost by mass
production using injection moulding. Accordingly, the present invention can be easily
applied to a relatively large-sized scanner.
[0103] It is important to design the waveguide array in the present invention such that
the distance between the object and the detector is small. Namely, in the design of
the optical scanner, a width W of the optical scanner as shown in Fig. 22a can be
calculated by the following formula.
![](https://data.epo.org/publication-server/image?imagePath=2003/37/DOC/EPNWB1/EP96305150NWB1/imgb0004)
Here, s' is the distance between a lens and a waveguide and
r is the radius of curvature of a bent portion of the waveguide. Further,
n is the total number of waveguides and
a is the width of the waveguide. Further,
b is the minimum clearance of the waveguides and D is the diameter of the lens on the
input face. When the relation between the scanner width W and a bending angle γ of
the bent portion of the waveguide is calculated by the above formula, it should be
understood that the scanner width is greatly changed in accordance with the bending
angle γ of the bent portion of the waveguide as shown in Fig. 23a. In this embodiment,
for example, s' is 548 µm, r is 1 mm, n is 2048, a is 8 µm, b is 6 µm, and D is 125
µm. Fig. 23b enlargedly shows a graph near a minimum portion of the scanner width
shown in Fig. 23a. As can be clearly seen from the graphs of Figs. 23a and 23b, the
scanner width in the present invention has a minimum value when the bending angle
of the bent portion of the waveguide is set to 90 degrees. Namely, when the distance
between the object and the detector is minimized, it is sufficient to use each of
two 90 degree curves in the bent portion of the optical waveguide.
[0104] It is clear from the graph of Fig. 23a that the scanner width is narrower than 83
mm when the bending angle of the bent portion of the waveguide is greater than 62.1
degrees and is less than 117.9 degrees. Namely, the minimum scanner width is 83 mm
in the case of the general optical scanner in which an optical system is folded by
using three mirrors. Accordingly, the present invention is effective to further reduce
this scanner width. Therefore, in the optical scanner of the present invention, the
bending angle of the bent portion of each waveguide is set to be greater than 62.1
degrees and less than 117.9 degrees.
[0105] Fig. 22a clearly shows the construction using each of two 90 degree curves in the
bent portion of this optical waveguide. The waveguide comes in contact with both input
and output faces of the optical scanner at 90 degrees. Thus, it is ensured that the
optical scanner size is minimized and coupling efficiency is maximized. The waveguide
has a size selected such that light throughput is maximized and interference and crosstalk
between adjacent waveguides are minimized. Concretely, the size of the waveguide is
selected as follows.
[0106] The array of microlenses can be fabricated by many methods. For example, the microlens
array can be fabricated by ion diffusion within glass or by reactive ion etching of
glass. The microlens array is attached to the substrate in alignment with waveguides
by using optical epoxy, etc.
[0107] In a preferable embodiment, the microlens array can be simultaneously formed by using
the same injection moulding method as the injection moulding method used to form the
grooves in the polymeric substrate. This method has distinct advantages. The main
advantage of this method is that it is not necessary to align the lens array and the
microlens array after the optical scanner is fabricated. When a mould is prepared
in an injection moulding process, the shape and position of the microlenses and waveguides
are set. The microlens array and the plastic substrate having a groove aligned in
advance with the microlens array are fabricated as one unit. In other advantages of
the above injection moulding method, the optical scanner is easily manufactured in
comparison with two units and optical performance is improved and stability of operation
of the optical scanner is increased.
[0108] The microlens array is designed such that each of the image portions is converged
to a separate waveguide. Further, only light scattered from a portion of the scanned
object is coupled into the waveguide by setting the numerical aperture of the microlens
to be equal to that of the optical waveguide. The other light incident on waveguide
is not coupled into this waveguide since the other light has angles greater than the
coupling angle of the waveguide. An output face of the waveguide array is mechanically
polished and a CCD array is aligned with this output face and is attached onto this
output face using optical epoxy, etc.
[0109] A compact optical scanner of the present embodiment will next be explained with reference
to Figs. 22a to 22c. This compact optical scanner is used in a G3 type facsimile machine
having 256 mm in width and suitable for a paper sheet size until B4 with a resolution
of 200 d.p.i. (dot/inch) as a concrete example. In Figs. 22a to 22c, reference numerals
201, 203 and 205 respectively designate an object to be read, a CCD detector and a
microlens array. Reference numerals 206 and 207 respectively designate a substrate
having optical waveguides and an LED array for illuminating the object. A Citizen
Electronics SNK-06A-27LED array is used as a light source. This light source requires
a 24 V power supply and emits light at 570 nm. A NEC µ PD3743DCCD line sensor is used
as the optical detector. This sensor includes 2048 pixels with a spacing of 14 µm.
[0110] A polymethyl methacrylate (PMMA) material called Acrypet VH (supplied by Mitsubishi
Rayon K.K., Japan) is selected to fabricate the substrate. This material has a refractive
index of 1.492 at 570 nm in wavelength and 20°C and further this material has high
optical transparency and is very suitable for injection moulding. A waveguide core
material is formed using a dimethyl carbonate based material called RAV7 H1 (supplied
by Mitecs K.K., Japan). This core material can be polymerized by heating in the presence
of benzoyl peroxide. The polymerized core material has a refractive index of 1.503
at 570 nm in wavelength and 20°C. This polymerized core material also has excellent
optical characteristics. The numerical aperture (N.A.) of the optical waveguides fabricated
by these materials is 0.181.
[0111] The microlens array is designed such that each microlens is 125 µm in diameter. This
design corresponds to a specification of 200 d.p.i. The lens is designed such that
this lens has a numerical aperture of 0.181 to match that of the waveguide. A focal
length f of such a lens can be calculated by the following standard formula in which
D is the lens diameter.
![](https://data.epo.org/publication-server/image?imagePath=2003/37/DOC/EPNWB1/EP96305150NWB1/imgb0005)
[0112] The focal length is 345 µm from the above formula.
[0113] A radius of curvature of the microlens can be also calculated by using the Gaussian
formula for a single spherical surface.
![](https://data.epo.org/publication-server/image?imagePath=2003/37/DOC/EPNWB1/EP96305150NWB1/imgb0006)
[0114] Here,
n is the refractive index of air and n' is the refractive index of each of the lens
and the polymeric substrate. In this case, the lens is fabricated from Acrypet VH.
Further,
n is set to 1.0 and n' is set to 1.492. In Fig. 24, a converging distance s is set
to a focal length (345 µm) of the microlens and the distance s' from a corresponding
lens to a waveguide is set to infinity. In this case,
r is equal to 170 µm by calculating the above formula. The lens focuses and forms an
image portion having 125 µm in length on an input face of the waveguide. Since the
waveguide is 8 µm in diameter, it is necessary to reduce the image by the lens at
a rate of 15.6. Magnification
m is given from simple geometrical optics shown in Fig. 24 by the following formula.
![](https://data.epo.org/publication-server/image?imagePath=2003/37/DOC/EPNWB1/EP96305150NWB1/imgb0007)
[0115] Accordingly, the values of
s and s' are respectively 5.74 mm and 548 µm by using this formula and the Gaussian
formula for a single spherical surface.
[0116] The waveguide is designed with a width of 8 µm and a minimum spacing of 6 µm. The
pitch of the waveguides is set to 14 µm on an interface with the CCD detector and
is set to 125 µm on an input face. The waveguides come in contact with both the input
and output faces to ensure maximum coupling efficiency.
[0117] When each of the optical waveguides is bent, some optical loss is inherently caused.
However, this loss can be made negligible by increasing the radius of curvature (ROC)
of a bent portion as follows.
![](https://data.epo.org/publication-server/image?imagePath=2003/37/DOC/EPNWB1/EP96305150NWB1/imgb0008)
[0118] Here, N is the effective refractive index of the waveguide, λ is the wavelength and
a is the waveguide width. In this case, if N is 1.503 and the refractive index n of
a clad is 1.492 and a changing amount of the refractive index is 0.011, a minimum
radius of curvature (ROC) corresponds to about 200 µm. A value of 1.0 mm is selected
as the curvature radius to completely eliminate this loss. When these parameters are
used, an overall width of the waveguide device is 16.9 mm.
[0119] Then, a master mould is fabricated as mentioned above by using the design criteria
calculated so far. This mould can be manufactured with high accuracy by ion milling
a nickel plate using standard techniques. This master is used in a standard injection
moulding machine to manufacture an Acrypet VH polymer substrate 2mm in thickness and
including a waveguide groove. Then, RAV7HI is mixed with 5 % of benzoyl peroxide and
is degassed for 15 minutes under a vacuum of 10
-4 Torr. This mixture is spread on the moulded substrate such that the groove is completely
filled with the mixture. A second flat VH polymer substrate is placed and fixed onto
this mixture. A fixed unit is then placed in an oven at 80°C for 6 hours to polymerize
the RAV7HI core material.
[0120] The output face of the waveguide is polished by using a standard polishing machine
(Musashino Denshi MA300) with alumina suspension down to 0.1 µm in size. The CCD unit
is then aligned and is butted to the waveguide array and is fixed by using an optical
grade epoxy (Lens Bond, Summers Laboratories, USA) so that the optical scanner is
completely manufactured.
[0121] In accordance with a preferred embodiment of the present invention, plural optical
waveguides for transmitting an inputted image to CCD elements are included within
a substrate formed by a polymeric material. Each of the waveguides is constructed
from a polymer having a refractive index higher than that of the substrate material.
Each of the waveguides has two bent portions having a bending angle of 90 degrees
and is vertically arranged on a substrate face opposite to an object and a face with
aligned CCD elements at both ends of each of the waveguides. Accordingly, even when
the image reduction ratio is large, the distance between the object and a detector
can be made small.
[0122] Accordingly, the embodiment invention can provide a compact scanner which can increase
the reduction ratio and reduce the distance between the object and the detector and
has a simple structure that can be manufactured easily and cheaply.
[0123] In accordance with the present invention, plural optical waveguides for transmitting
an inputted image to CCD elements are included within a substrate formed by a polymeric
material. Each of the waveguides is constructed from a polymer having a refractive
index higher than that of the substrate. Each of the waveguides has two bent portions
having a bending angle greater than 62.1 degrees and less than 117.9 degrees. Each
of the waveguides is vertically arranged on a substrate face opposite to an object
and a face with aligned CCD elements at both ends of each of the waveguides. Accordingly,
even when the image reduction ratio is large, the distance between the object and
a detector can be made small.
[0124] Accordingly, the present invention can provide a compact scanner which can increase
the reduction ratio and reduce the distance between the object and the detector and
has a simple structure that can be manufactured easily and cheaply.
[0125] In accordance with a preferred embodiment of the present invention, a microlens integrated
with the substrate is arranged in alignment with an end portion of each of the optical
waveguides on the substrate face opposite to the object so that each of image portions
can be reliably converged to each of the waveguides.
[0126] In accordance with a preferred embodiment of the present invention, the numerical
apertures of the microlens and the polymer of each of the optical waveguides are set
to be equal to each other. Accordingly, it is ensured that only light scattered from
a scanned image portion is coupled into each of the waveguides.
[0127] A waveguide type reduction type image sensor in another example will next be explained
with reference to Figs. 25 to 31.
[0128] Firstly, the manufacturing method of a patterned substrate will be explained in detail
with reference to Figs. 26a to 26e. As shown in Fig. 26a, a photoresist film 502 having
8 µm in thickness is first formed on a PMMA substrate 501. As shown in Fig. 26b, a
groove pattern is next transferred by photolithographic techniques. Namely, a mask
503 comes in close contact with this photoresist film 502 and the photoresist film
502 and the mask 503 are exposed to an ultraviolet ray 511. When developing processing
is then performed, the groove pattern of the mask 503 is transferred to the photoresist
film 502. Thus, as shown in Fig. 26c, the photoresist film 502 of the groove pattern
is formed. This groove is also 8 µm in width in this example. Next, as shown in Fig.
26d, ions 512 are irradiated onto a surface of the patterned photoresist film 502
by an RIE etching method so that a groove having 10 µm in depth is formed in a substrate
portion having no resist film. Finally, the photoresist film 502 is dissolved by using
a resist separating agent so that a patterned PMMA substrate having the groove as
a capillary having 8 µm in width and 10 µm in depth is manufactured as shown in Fig.
26e.
[0129] As shown in Fig. 25a, the groove processed in the example is set to the pattern of
a reduction type optical waveguide having two bent portions. A groove 402 for reducing
loss of an optical signal in the bent portions is adjacent outside each of the bent
portions of the optical waveguide 401. Fig. 25b is an enlarged view showing each of
the bent portions and the adjacent groove in detail. For example, the groove 401 as
the optical waveguide is 8 µm in width w and the interval d between this groove and
the adjacent groove 402 is 2 µm. The adjacent groove 402 is 2 µm in width u and a
bent portion of the groove 401 is 200 µm in curvature radius R. Each of the grooves
for the optical waveguide reach both ends of the PMMA substrate. In contrast to this,
the adjacent groove 402 not reaching the PMMA substrate ends at either end is arranged
such that this adjacent groove 402 has a bent portion formed in a concentric arc shape
outside each of the bent portions of the grooves 401 of the optical waveguides.
[0130] Secondly, a process for making the patterned substrate manufactured as above come
in close contact with a plane substrate will be explained with reference to Figs.
27a and 27b. As shown in Fig. 27a, the patterned substrate 501 and the plane substrate
601 are set inside a jig 610 for clamping and come in close contact with each other
using this jig for a clamp. Thus, the grooved portion of the patterned substrate 501
is formed in the shape of a cavity so that a capillary 602 is formed. As shown in
Fig. 27b, three side faces of the clamped substrates except for a side face having
one open portion of the capillary 602 as the suction port for the monomer are sealed
by using seal resin 603 for a low vacuum formed by epoxy resin, etc. Thus, the other
open portion not constituting the monomer suction port of the capillary 602 is also
sealed. The groove not reaching the PMMA substrate ends at both ends thereof attains
a state in which the air is sealed within the cavity of this groove.
[0131] Thirdly, a process for filling the capillary formed by making the pattern and plane
substrates come in close contact with each other as mentioned above with a monomer
solution as the core raw material will next be explained with reference to Figs. 28a
and 28b. The patterned substrate 501 and the plane substrate 601 clamped by the clamping
jig 610 are set in a holder 701 within a vacuum chamber 710 as shown in Fig. 28a.
The holder 701 is constructed such that the clamping jig 610 can be moved in the vertical
direction. A container 702 filled with the monomer solution of allyl diglycol carbonate
(RAV7) including 5 % of benzoyl peroxide is arranged within the vacuum chamber 710
such that this container is located just below the clamping jig 610. The benzoyl peroxide
included in the RAV7 monomer solution acts as a catalyst for polymerizing the RAV7
monomer when the benzoyl peroxide is heated. Next, the vacuum chamber 710 is evacuated
to a vacuum of 10
-4 Torr so that the RAV7 monomer solution is degassed and the gases within the capillary
opened at one end thereof are removed therefrom. Thereafter, the clamping jig 610
is moved in a downward direction by using the holder 701 and the open portion of the
capillary is dipped into the RAV7 monomer solution. Then, when the interior of the
vacuum chamber 710 is leaked such that the pressure within the vacuum chamber is gradually
changed from a vacuum to atmospheric pressure, the pressure within the capillary is
less than the circumferential pressure of the RAV7 monomer solution so that the RAV7
monomer solution is sucked into the capillary. In this way, when a relative long capillary
is filled with the monomer, the filling process of the monomer into the capillary
can be performed if a change in pressure using the vacuum is utilized such that effects
obtained by the capillary phenomenon are supported. No groove sealed at both ends
thereof is filled with the monomer solution so that this groove is still filled with
gases.
[0132] Finally, after the interior of the capillary is filled with the RAV7 monomer solution
and the pressure within the vacuum chamber reaches atmospheric pressure, the clamping
jig 610 is detached from the holder 701 and the RAV7 monomer solution is heated for
6 hours at a temperature of 85°C by using an oven so that the RAV7 monomer solution
is polymerized. The surface of a polymeric optical waveguide manufactured as above
is polished by a standard polishing device using a diamond suspension having a size
equal to or smaller than 0.5 µm so that the seal resin is removed from this surface.
Thus, the polymeric optical waveguide in the present example can be manufactured.
[0133] Light from a laser is incident on the incident end of a core of the polymeric optical
waveguide manufactured as above. Light emitted from this polymeric optical waveguide
is measured and transmission loss in the optical waveguide is calculated.
[0134] As a result, 55 % of light is transmitted through an optical waveguide having 200
µm in curvature radius and having no adjacent groove. However, 92 % of light is transmitted
through an optical waveguide having 200 µm in curvature radius and having a groove.
[0135] Fig. 29 is a graph showing reducing effects of light loss in the polymeric optical
waveguide manufactured in the example when the width of a groove arranged outside
the bent portion of a waveguide core portion and shown by u in Fig. 25b is changed.
In Fig. 29, the axis of ordinate shows the ratio of the emitting intensity of light
from the waveguide for the case with the groove to an emitting intensity of light
from the waveguide for the case without the groove. Namely, if the value of this ratio
on the axis of ordinate is greater than one, there are effects of the groove arranged
outside the bent portion of the waveguide core portion. Further, these effects are
increased as this ratio value is increased. The waveguide core portion is set to have
8 µm in width and the distance between the groove and the waveguide core portion is
set to 2 µm. It is known from Fig. 29 that the width u of the groove arranged outside
the bent portion of the waveguide core portion is suitably set to be equal to or smaller
than 2 µm in view of compactness of the waveguide and the reducing effects of light
loss. In this example , this groove width is set to 2 µm since it is difficult to
finely process the groove.
[0136] Fig. 30 is a graph showing the reducing effects of light loss in the polymeric optical
waveguide manufactured in the example when the distance d in Fig. 25b between the
waveguide core portion and a groove arranged outside the bent portion of the waveguide
core portion is changed. In Fig. 30, the axis of ordinate shows the same contents
as Fig. 29. The waveguide core portion is 8 µm in width and the groove is 2 µm in
width. It is known from Fig. 30 that the distance d between the waveguide core portion
and the groove arranged outside the bent portion of the waveguide core portion is
suitably set to be equal to or smaller than 2 µm in view of compactness of the waveguide
and the reducing effects of light loss. However, this distance is set to 2 µm in the
example since it is difficult to finely process the groove and the waveguide core
portion.
[0137] Fig. 31 is a graph showing the reducing effects of light loss in the polymeric optical
waveguide manufactured as above when the difference in specific refractive index between
the waveguide core portion and the material of a clad portion is changed. In Fig.
31, the axis of ordinate shows the same contents as Fig. 29. It is known from Fig.
31 that it is suitable to select materials of the core and the clad in view of the
reducing effects of light loss such that the difference in specific refractive index
between the core and the clad is smaller than 1.5 %. In the example , materials of
the core and the clad providing 0.86 % as the difference in specific refractive index
are used.
[0138] In this example, a gas filled into the groove adjacent to the bent portion of the
optical waveguide is constructed by air. However, the groove adjacent to the bent
portion can be filled with various kinds of gases other than air by sticking the patterned
substrate and the plane substrate to each other within a gaseous environment other
than air. Accordingly, the gas filled with this groove is not limited to air in the
present example.
[0139] Further, materials of the clad and core portions are not limited to the above materials
in this example, but can be constructed using various materials in a combination so
that the difference in specific refractive index is smaller than 1.5 %.
[0140] In accordance with the waveguide type reduction type described above, it is possible
to reduce light loss caused when light is transmitted through the bent portion of
a waveguide. Accordingly, light transmittance of the waveguide can be increased.
[0141] A groove can be easily filled with a gas by manufacturing this image sensor within
a gaseous environment.
[0142] Light loss in the bent portion can be effectively reduced when the waveguide is made
compact.
[0143] Light loss in the bent portion can be effectively reduced when the waveguide is made
compact.
[0144] Light loss in the bent portion can be further effectively reduced when sizes, etc.
of the waveguide and the groove are set to be equal to each other.
[0145] In accordance with a manufacturing method as described above , the optical waveguide
and the groove can be easily filled with respective materials having different refractive
indexes. Further, the optical waveguide can be very simply manufactured by using this
manufacturing method.